Re: [PATCH v2] trace/trace_event_perf: remove duplicate samples on the first tracepoint event
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From: Yeo Reum Yun <hidden>
Date: 2024-10-01 08:49:25
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Gentle ping in case of forgotten. ________________________________________ From: Steven Rostedt <rostedt@goodmis.org> Sent: 26 September 2024 13:51 To: Yeo Reum Yun Cc: mhiramat@kernel.org; mathieu.desnoyers@efficios.com; a.p.zijlstra@chello.nl; mingo@elte.hu; Mark Rutland; james.clark@linaro.org; nd; linux-kernel@vger.kernel.org; linux-trace-kernel@vger.kernel.org; Peter Zijlstra; Frederic Weisbecker; Arnaldo Carvalho de Melo; Namhyung Kim Subject: Re: [PATCH v2] trace/trace_event_perf: remove duplicate samples on the first tracepoint event Can one of the perf folks give me an Ack, and I'll take this through my tree. -- Steve On Fri, 13 Sep 2024 03:13:47 +0100 Levi Yun [off-list ref] wrote:
quoted hunk ↗ jump to hunk
When a tracepoint event is created with attr.freq = 1, 'hwc->period_left' is not initialized correctly. As a result, in the perf_swevent_overflow() function, when the first time the event occurs, it calculates the event overflow and the perf_swevent_set_period() returns 3, this leads to the event are recorded for three duplicate times. Step to reproduce: 1. Enable the tracepoint event & starting tracing $ echo 1 > /sys/kernel/tracing/events/module/module_free $ echo 1 > /sys/kernel/tracing/tracing_on 2. Record with perf $ perf record -a --strict-freq -F 1 -e "module:module_free" 3. Trigger module_free event. $ modprobe -i sunrpc $ modprobe -r sunrpc Result: - Trace pipe result: $ cat trace_pipe modprobe-174509 [003] ..... 6504.868896: module_free: sunrpc - perf sample: modprobe 174509 [003] 6504.868980: module:module_free: sunrpc modprobe 174509 [003] 6504.868980: module:module_free: sunrpc modprobe 174509 [003] 6504.868980: module:module_free: sunrpc By setting period_left via perf_swevent_set_period() as other sw_event did, This problem could be solved. After patch: - Trace pipe result: $ cat trace_pipe modprobe 1153096 [068] 613468.867774: module:module_free: xfs - perf sample modprobe 1153096 [068] 613468.867794: module:module_free: xfs Fixes: bd2b5b12849a ("perf_counter: More aggressive frequency adjustment") Signed-off-by: Levi Yun <redacted> --- Changes in v2: - Fix build error. --- kernel/trace/trace_event_perf.c | 6 ++++++ 1 file changed, 6 insertions(+)diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c index 05e791241812..3ff9caa4a71b 100644 --- a/kernel/trace/trace_event_perf.c +++ b/kernel/trace/trace_event_perf.c@@ -352,10 +352,16 @@ void perf_uprobe_destroy(struct perf_event *p_event) int perf_trace_add(struct perf_event *p_event, int flags) { struct trace_event_call *tp_event = p_event->tp_event; + struct hw_perf_event *hwc = &p_event->hw; if (!(flags & PERF_EF_START)) p_event->hw.state = PERF_HES_STOPPED; + if (is_sampling_event(p_event)) { + hwc->last_period = hwc->sample_period; + perf_swevent_set_period(p_event); + } + /* * If TRACE_REG_PERF_ADD returns false; no custom action was performed * and we need to take the default action of enqueueing our event on --LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}